Thermal stability additive in hydrocarbon jet fuels



United States PatentOffice 2,945,342 Patented July 19, 1960 THERMALSTABILITY ADDITIVE IN HYDROCARBON JET FUELS Robert M.SchirmenBartlesville, kla., assignorto Phillips Petroleum Company, acorporation of Delaware No Drawing. Filed May 9, 1958, Ser. No. 734,121

7 Claims. (Cl. 60--35.4)

This invention relates to an improved fuel. In another aspect it relatesto a method of increasing the thermal stability of a jet or rocket fuelby incorporating an add tive therein. In still another aspect thisinvention relates to a method of operating a jet or rocket engine inwhich the fuel before combustion is subjected to high temperatures. 7

Jet engines including both the ram jet and turbo jet types operate onthe thrust delivered when fuel is sprayed into a combustion chamber andburned continuously in a confined space. The hot products of combustionexhaust through a tube extending rearwardly from the engine. Many typesof rocket engines operate on the same principle except that the requiredoxygen is supplied independently of the atmosphere. iln aircraft ormissiles which achieve supersonic speeds the, fuel is subjected torelatively high temperatures as it passes through the conduits from thestorage tanks to the combustion chamber. For example, at a speed of Mach2 the air entering a jet engine is at a temperature of about 400 F.while at a speed of Mach 4 the ram air temperature would reach 1000" F.Also in some engines, jet fuel is used to cool the lubricant oil therebyadding more heat to the fuel. Some fuels are unstable at hightemperatures and deposits form in the fuel lines tending to plug thenozzles in the combustion zone. 'At temperatures up to about 400 F. manyof the usual detergent-disperant type additives are effective inalleviating the problems of deposits and 'filterability. However, athigher temperatures the usual detergent-dispersant type additives tendto promote deposit formation and plug fuel system filters.

I have discovered that the thermal stability of jet or rocket fuels canbe' improved by incorporating therein an extract from an oily carbonblack. By forming a furnace black having a photelometer reading lessthan 50, extracting the oily deposit with a suitable solvent and addingfrom 1 to 1000 parts per million of this extract to a jet type-fuel, thethermal stability of the fuel at temperatures above 400 F., can beimproved. By practicing my invention a jet or rocket engine can beoperated under conditions which subject the fuel in the fuel lines totemperatures above400 F. with the problems of filter pluggingconsiderably reduced.

It is an object of my invention to provide an improved fuel. Anotherobject is to provide 'an additive which can be incorporated into a jetor rocket fuel to improve its thermal stability. Still another object ofmy invention is to provide a method by which thermal stability of a jetfuel can be improved Another object is to provide a method of operatinga jet 'or rocket engine under conditions which subject the fuel in thefuel lines to temperatures above 400 F. Other objects, advantages andfeatures of my invention will be apparent to those skilled in the artfrom the following disclosure and claims,

A wide range of fuel compositions can be employed in jet engines. Ingeneral, the jet fuel should possess a low freezing point, burn With astable flame, be non-corrosive, not form coke upon combustion, and havea high B.t.u. content per gallon. Jet fuels are generally hydrocarbonsin the gasoline and kerosene boiling range and can be obtained fromcrude oil, gas oil, residual oils, shale oils, tars, or the like. Myinvention can be employed with both leaded and non-leaded fuels and thefuel can con tain other additives such as various phosphorus compoundsto improve its stability or performance. A set of specifications whichindicate the general properties of a typical jet fuel is as follows:

1. Freezing point -40 C. max. 2. Kinematic viscosity 6 centistokes max.18 C. 3. Flash point 38 C. min. 4. Sulfur content 0.20% by Wt. max. 5.Corrosion Only slight discoloration of copper strip. 6. Gravity Nospecification. 7. Accelerated gum 20 mg./ ml. max. 8. Residue (air-jetmethod)". 10 mg./ 100 ml. max. 9. Aromatics content 20% max. 10. Watertolerance Substantially immiscible. ll. Distillation:

' Percent olf at 410 F 10% min.

Final B. Pt., F 550-600. Loss 1 /2% max. 12. Heat of combustion 18,300B.t.u./1b., min.

The above specifications have been considered satisfactory by commercialairlines. Other specifications for jet aircraft fuels 7 include those ofMIL-F-5624C and MIL-P-25656 (USAF). While some jet fuels are inherentlymore thermally stable than others, it is Within the scope of myinvention to improve the thermal stability of any jet aircraft type fuelby adding thereto the carbon black extract described.

Rocket fuels for which my invention can be used are ofthe same generaltype as the jet fuels described above, being generally hydrocarbons ofhigh B.t.u. content. Kerosene is a suitable rocket fuelwhen used with anoxidant such as liquid oxygen or hydrogen peroxide. The fuel and oxidantcomprise what is known as -a bipropellant. To obtain the additive for myinvention carbon black is formedin a furnace'with partial combustion sothat a tarryor oilyblack is the product. Many different kinds of. fuelscan be used to make such a carbon black. For example, adegraded recyclegas oil can be employed, or other oils, such as kerosene, gasolineboiling range hydrocarbons, light or heavy naphthas, or heavier oilsare. satisfactory. Other hydrocarbon materials such as natural gas orrefinery residue gas can be used. Broadly, any hydrocarbon can be usedas the furnace feed and the charge stocks can contain saturated'orunsaturated hydrocarbons, parafiins, olefins, aromatics, naphthenes, orthe like, I prefer to employ carbon black whichhas been formed from ahighly. aromatic fuel, such as S0 extract oil oran aromatic cycle oilfrom catalytic cracking. Whatever the fuel that, is used, the conditionsof furnace operation can be controlled by those skilled in thisart toproduce a suitable black by partial combustion. The carbon blackemployed for my invention should have a photelometer reading less than50 and preferably less than 20. Dily blacks having a photelometerreading. of about 10 are highly'satisfactory. A photelometer reading ofa carbon black is an indica tion of the tar content of the black asdetermined by the amount of light which a standard sample of achloroform extract transmits. The tar content of the carbon black isdetermined by mixing 2 grams of black with 50 cc. of chloroform, boilingthe mixture, filtering out the carbon black, and determining thepercentage of light transmittance of the filtrate as compared with thetransmittance of a blank sample of chloroform. The comparison ispreferably conducted with a photoelectric colorimeter. Thev photelometerreading is the percentage of light transmittance.

The fuel additive is obtained from the oily black by any suitablesolvent, preferably using a solvent which can be added directly to thefuel without deleterious effects. Most hydrocarbon solvents are suitableand even chloroform can be used if the additive is recovered bydistillation and redissolved in a solvent for adding to the fuel.Suitable solvents include kerosene, benzene, toluene, naphtha,cyclohexane, methylcyclohexane and the like.

Sufficient extract or solution should be added to the fuel in order toprovide from 1 to 1000 parts of additive per million parts of fuel on aweight basis. Preferably, for best results in improved thermal stabilityand overall performance, the amount of additive in the fuel should be inthe range of about 1 to 100 parts per million. The additive itself whichis extracted from the carbon black is a brown, waxy material which boilsabove 600 F.

In the operation of a jet or rocket engine according to my invention afuel is employed which contains the abovedescribed additive in theprescribed amount. This fuel can be subjected to temperatures above 400F. and then passed through the filters and nozzle of the fuel systeminto the combustion chamber. In addition to improving the thermalstability of the fuel by reducing deposits and improving filterability,the additive of my invention has the added advantage over many otheradditives for this purpose in that it is insoluble in water and thuswill not be leached out of the fuel when the fuel is stored over water,as is often done on aircraft carriers. Also, my additive increases theelectrical conductivity of the fuel, thereby reducing the possibility ofbuilding up static charges of electricity in the fuel as it flowsthrough the fuel lines.

Advantages of this invention are illustrated by the following examples.The reactants, and their proportions, and other specific conditions arepresented as being typical and should not be construed to limit theinvention unduly.

Example I Carbon black (a soft furnace black) produced from a highlyaromatic heavy residuum and having a photelometer reading of 10 percentwas extracted with kerosene to recover the tarry additive employed inthis invention. One hundred (100) grams of the oily carbon black wasextracted with 1600 milliliters of kerosene up to 600 F. A non-volatileresidue which was a brown, dry, waxy material was recovered in an amountindicating a concentration of 700 milligrams of additive per liter ofkirosene solution formed on extraction of the carbon blac Two hundredfifteen (215) milliliters of this solution was added to gallons ofkerosene to give about p.p.m. of additive in the fuel. Three runs weremade to determine the thermal stability of this kerosene, two runswithout the additive (runs 2 and 3) and one run with the additive in theconcentration of 10 ppm. (run 1). The test procedure was the TentativeStandard Method 3464-T (June 1, 1957), for Thermal Stability of GasTurbine Fuels (part of Federal Test Method Standard No. 791 anddescribed in the Coordinating Research Council, Inc. Manual No. 3). Themanual operating procedure was used with the CFR Fuel .Coker. Resultswere as follows:

Filter Block Total Test Time (Minutes) Time to Pressure Drop (Minutes)Additive (pr- Preheater Rating Run Fuel Pressure (inches of Hg)Kerosene... do do CDO oro NNM more The above data show a markedimprovement in the thermal stability of the fuel containing the carbonblack extract. Pressure drop through the filter didnt approach themaximum for the full duration of the test for the fuel containing myadditive while the preheater rating remained high. In contrast, fuelwithout the additive reached maximum pressure drop in less than half therun time.

The kerosene used had the following specifications:

Flash point, F. 142 Gravity, API 41.7 ASTM distillation, F.:

IBP 5% 10% 20% 40% 50% 0% End point 52,7 Recovery, percent 99 Sulfur,weight percent 0.024 Mercaptan sulfur, weight percent Neg. Copper stripcorrosion Neg. Color ,+28 Smoke point, millimeters of flame height 19.5

Example II An oily carbon black was produced by passing a S0 extract oilinto a porous combustor. The combustor can, which was 9 /2 inches longwith an internal diameter of 2 inches, was constructed of porousstainless steel. The primary air inlet system consisted of four rows ofA-inch holes, each row consisting of six holes equally spacedcircumferentially around the can. The distance from the edge of the canto the center of the first row of holes was one inch, and subsequentrows were spaced at 1%- inch center to center. Quench air enteredthrough two rows of holes, each consisting of six /2-iuch holes equallyspaced circumferentially around the can, these rows continuing the 1/z-inch center-to-center spacing of the primary air holes. Air,preheated to 500 F., was fed at a rate of one pound per second.Unpreheated oil was fed axially through a 29 gal/hour Monarch nozzle ata rate of 180 pounds per hour. The total air and oil feed to the reactorwas fuel rich, and produced a carbon black having a photelometer readingof about 10.

Two grams of the above described oily black was extracted with cubiccentimeters of kerosene using successive 10 cc. washings. The solutionextract was then added to 5 gallons of kerosene and the resulting fuelwas tested for thermal stability as described in Example I except thatthe recirculation method was used with a one quart sample. The fuel flowrate was 6 pounds per hour and the test time was 2 hours. The preheatertemperature was 450 F. and the filter black temperature was 550 F. Tworuns were made with the same fuel without the additive of my invention.The preheater rating of all runs was 4 on the Coordinating ResearchCouncil scale. Using a rating method which takes into accountappearance, quantity and location of preheater deposits, the fuelcontaining my additive showed considerable improvement in this area. Ona scale of zero to one hundred, zero being 100 percent coverage by blacklacquer and one hundred being 100 percent clean, the preheater rating ofthe two fuels containing no additive was 58 and 58.3 while the rating ofthe fuel containing the carbon black extract was 71.5. This rating ismade by evaluating each of four equal segments along the length of thepreheater tube, multiplying each rating by a weighting factor, andadding the products to arrive at the final rating. The rating of eachsegment is obtained by multiplying the fraction of each segment coveredby a particular deposit times a number assigned that deposit identity.These numerical ratings are as follows:

Deposit identity: Numerical rating Clean 10.0 Light amber lacquer 7.5Medium amber lacquer 5.5 Dark amber lacquer 4.0 Light brown lacquer 2.8Medium brown lacquer 1.9 Dark brown lacquer 1.2 Light black lacquer 0.7.Medium black lacquer 0.3 Black lacquer 0.0

The weighting factors for segments 1 through 4, segment 1 being nearestthe fuel inlet and 4 being nearest the outlet, are as follows:

Segment 1 Segment 2 Segment 3 Segment 4 A pressure drop of 25 inches ofmercury across the filter was reached in 29.3 and 29.8 minutes for thefuel without my additive. With the kerosene containingthe additive, apressure drop of 25 inches of mercury across the filter was reached in71.5 minutes. It is thus evident that the additive is responsible for aconsiderable improvement in filterability of the fuel.

As will be evident to those skilled in the art, various modifications ofthis invention can be made, or followed, in the light of the foregoingdisclosure and discussion, without departing from the spirit or scopethereof.

I claim:

1. A method of operating a reaction engine in which the fuel issubjected to elevated temperatures before combustion which comprisessupplying to said engine a hydrocarbon fuel containing as an additivefrom 1 to 1000 parts per million of the hydrocarbon soluble extract froman oily carbon black which before extraction had a photelometer readingless than 50, subjecting said fuel to a temperature in excess of 400 F.prior to combustion, and burning said fuel in the combustion chamber ofsaid engine.

2. A method of operating a reaction engine in which the fuel issubjected to elevated temperatures before combustion which comprisessupplying to said engine a hydrocarbon fuel containing from 1 to partsper million of the hydrocarbon soluble extract boiling above about 600F. obtained from an oily carbon black which before extraction had aphotelometer reading below 20, subjecting said fuel to a temperature inexcess of 400 F.

prior to combustion, and burning said fuel in the combustion chamber ofsaid engine.

3. A hydrocarbon jet fuel having improved thermal stability containingfrom 1 to 1000 parts per million of the hydrocarbon soluble extract froman oily carbon black which before extraction had a photelometer readingless than 50.

4. A hydrocarbon jet fuel having improved thermal stability containingfrom 1 to 100 parts per million of the hydrocarbon soluble extract froman oily carbon black which before extraction had a photelorneter readingless than 20, said extract being non-volatile, boiling above about 600F.

5. A hydrocarbon jet fuel according to claim 4 wherein said carbon blackis a furnace black prepared from a highly aromatic S0 extract oil.

6. A method of improving the thermal stability of a hydrocarbon jet'fuel which comprises adding to said fuel from 1 to 1000 pants permillion of the hydrocarbon soluble extract from an oily carbon blackwhich before extraction had a photelometer reading less than 50.

7. A method of improving the thermal stability of a hydrocarbon jet fuelwhich comprises adding to said fuel from 1 to 100 parts per million ofthe hydrocarbon soluble extract of an oily carbon black which beforeextraction had a photelometer reading less than 20, said extract boilingabove about 600 F.

References Cited in the file of this patent UNITED STATES PATENTS2,771,367 Thompson et a1 Nov. 20, 1956 2,771,368 Thompson et al. Nov.20, 1956 2,82A,791 Osborg et al. Feb. 25, 1958 2,849,301 Gee Aug. 26,1958

1. A METHOD OF OPERATING A REACTION ENGINE IN WHICH THE FUEL ISSUBJECTED TO ELEVATED TEMPERATURES BEFORE COMBUSTION WHICH COMPRISESSUPPLYING TO SAID ENGINE A HYDROCARBON FUEL CONTAINING AS AN ADDITIVEFROM 1 TO 1000 PARTS PER MILLION OF THE HYDROCARBON SOLUBLE EXTRACT FROMAN OILY CARBON BLACK WHICH BEFORE EXTRACTION HAD A PHOTELOMETER READINGLESS THAN 50, SUBJECTING SAID FUEL TO A TEMPERATURE IN EXCESS OF 400*F.PRIOR TO COMBUSTION, AND BURNING SAID FUEL IN THE COMBUSTION CHAMBER OFSAID ENGINE.